Gilliam, the deceased Second Prince and first son of the current Phoenix Tribe king, possessed blonde hair and scarlet eyes. He presented himself as a noble gentleman, upholding honor in combat and favoring sword-based fighting. A skilled swordsman, he wielded both a sentient Sword Being and ordinary swords. His abilities included manipulating blood-sucking flowers residing within his body; these flowers consumed his royal blood to grant him control. He also commanded Blood Warriors, such as the Sword Being and a bug-like entity deployed against Hime and Emile.

Distantly related to Fuhito and Duken, his siblings were Sylvia (eldest sister), Salieri, Emile, Severin, Hime, and Sherwood (all younger). His relationship with Hime was notably strained, despite once teaching her combat. He maintained a professional association with Flatirus, his personal android servant.

Gilliam orchestrated an assassination attempt against Hime. Hiro Hiyorimi's intervention thwarted this attempt. During this event, Gilliam observed Hiro possessed a unique connection to the Monster World, though the specifics remained undisclosed. This encounter was a significant interaction within the conflict among the royal siblings.